Major Vessels & Coronary Circulation

Here we are looking at Learning Objective 2.

Recognise and describe the major vessels that lie inside the chest and know their positions relative to each other

We are also looking at Learning Objective 9.

Locate and trace the 2 main coronary arteries and their major branches and know which regions of the heart each one supplies.

Major Vessels

Aorta

The aorta is the largest artery in the body, arises from the left ventricle as the ascending aorta (this gives rise to the left and right coronary arteries we will consider below) for 2 inches before forming the aortic arch. The arch extends from T2 to T4 level and bends over the pulmonary trunk. The aortic arch - moving right to left - gives rise to the brachiocephalic trunk, left common carotid and left subclavian artery. The aorta continues as the descending aorta from T4 to T12 level (also known as the thoracic aorta) and gives rise to bronchial, oesophageal, intercostal and subcostal arteries.

Diagram showing the aortic arch and its branches (from proximal to distal); brachiocephalic artery, left common carotid artery and the left subclavian artery.

Aorta segments and main branches.

Pulmonary Trunk

The pulmonary trunk is a thick short vessel separated from the right ventricle by the pulmonary valve. The trunk is located anteriorly and medially to the right atrium and it overlaps the root of the aorta and passes posteriorly. At the T5 level the trunk splits into the pulmonary arteries which take deoxygenated blood to the lungs. The right pulmonary artery is thicker and longer - both right and left pulmonary arteries divide into 2 branches.

Pulmonary trunk position relative to pulmonary veins, trachea and aorta.

Superior and Inferior Vena Cava

The superior vena cava is formed by 2 brachiocephalic veins coming together and travels inferiorly before draining into the superior portion of the right atrium at the level of the 3^rd rib. The base of the superior vena cava is hidden by the base of the aorta and the right auricle.

The inferior vena cava is formed by the iliac veins coming together, enters the pericardium at the level of T8 and drains into the inferior portion of the right atrium.

Diagram showing the key brachiocephalic veins that feed into the superor vena cava.

Veins feeding into the superior vena cava.

Coronary Circulation

Right Coronary Artery

Arises from the right aortic sinus and travels down the right coronary sulcus, curves posteriorly and makes a bend at the crux of the heart. It has 2 main branches; the right marginal artery and the posterior interventricular artery. The right coronary and right marginal arteries supply the right hand-side of the anterior surface. The posterior interventricular artery supplies the right hand-side posterior surface. The right coronary artery also has branches which supply the SA and AV nodes.

Left Coronary Artery

Arises from the left aortic sinus and passes between the pulmonary trunk and the left atrial appendage. Under the appendage, the artery divides into the left anterior descending artery and the left circumflex artery. Then progresses and forms the left marginal artery. The left anterior descending and left marginal arteries supply the left hand-side anterior surface. The left circumflex artery supplies the left-hand side posterior surface. The left anterior descending artery is referred to as the 'widow-maker' `because occlusion of this vessel is often fatal as it supplies the majority of the left ventricle.

Diagram showing the coronary circulation from the anterior and posterior views.

Anterior and posterior views of the coronary circulation.

Clinic Corner

Aortic Aneurysm

This describes dilation of the aorta to more than 1.5 times its original size. Although these are most common in the abdominal aorta, they can occur in the thoracic aorta. Often, these present with no symptoms but a rupture of the aneurysm is life-threatening and often fatal.

Comparison of thoracic and abdominal aortic aneurysms.

Coronary Heart Disease

Coronary heart disease (CHD) is one of the biggest killers in the UK. This refers to reduced blood flow to the myocardium due to narrowing of the blood vessels and can be caused by a whole host of factors including; high blood pressure, thrombosis (blood clots), diabetes, smoking and atherosclerosis (fatty plaques reduce vessel diameter). CHD can also have a number of consequences, the most severe of which is a myocardial infarction (heart attack) where occlusion of a blood vessel causes an infarction and necrosis of the heart myocardium. Blockages of vessels can be seen on coronary angiograms and treated with coronary angioplasty.

Storyboard showing how coronary angiograms are conducted with catheters and contrast agents.

Process of coronary angiography with catheter and contrast agents.

Image Credits: National Institutes of Health (USA) 2017, BruceBlaus 2015, National Institutes of Health (USA) 2016, The Goofy Anatomist 2017, University of Dundee 2011, OpenStax College 2013 - All Image Usage Complies with CC BY-SA 3.0.

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